1. Field of the Invention
This invention generally relates to an apparatus and method for heating a resorbable implant, and more particularly, to a method and apparatus for heating a resorbable implant which is reusable and provides a method for heating to thereby soften the resorbable implant prior to surgical implantation.
2. Discussion of the Related Art
The repair of separated or dislocated bone fragments or segments following bone surgeries sometimes requires realignment of the separated or dislocated fragments or segments and subsequent secure fixation for promoting proper natural rejoinder of these bone fragments or segments. The presence of relative motion of the bone fragments or segments at a fracture or osteotomy location may result in irritation of the surrounding tissues, nonunion between the bone fragments, and an extension of the time for fracture healing. It is therefore desirable to accomplish as completely as possible an immobilization of the fracture or osteotomy site. This involves the relative fixation of affected bone segments relative to each other and in relation to the surrounding bone structure.
Known methods for providing fixation between adjacent bone portions have included the use of metallic plates of varying configurations, which are secured across osteotomies or fracture sites by metallic bone screws. These devices have been made of biocompatible metals and metal alloys, such as commercially pure titanium, stainless steel and cobalt chrome molybdenum. Other materials and devices, such as wires, intramedullary nails or externally fixed pins have also been used to reduce bone fracture mobility and to improve the relative position of adjacent segments. The aim of fixation of adjacent bone portions is to immobilize the fracture or osteotomy sites in order to promote localized bone growth in the natural repair of the separation.
The use of medical implant devices made from bioresorbable materials has been described in literature and these devices have the advantage of being absorbed by the body over a period of time so as to allow for bone or fibrous material to become repaired at a fracture or osteotomy site by growing into the space created between adjacent bone portions. Many bioresorbable materials have been suggested for use in fixation of adjacent bone portions. It was believed that these materials had to be extremely strong to fixate the bone portions over a relatively long period of time. This typically meant that the osteosynthesis plate had to be relatively thick and be made out of a high molecular weight oriented material such as poly L-lactic acid in which the molecular weight would exceed 250,000. See Pihlajamaki, H., et al., xe2x80x9cAbsorbable Pins of Self-Reinforced Poly-L-Lactic Acid for Fixation of Fractures and Osteotomies,xe2x80x9d Journal of Bone and Joint Surgery, v. 74-B, n. 6, p. 853-857, November 1992. In addition, it was believed that certain copolymers of glycolide and lactide were not appropriate for use in osteosynthesis plates because of a rapid loss of mechanical strength. Grijpma, D. W., et al., xe2x80x9cPoly (L-lactide) Crosslinked with Spiro-bis-dimethylene-carbonate,xe2x80x9d Polymer, v. 34, n. 7, 1993 at 1496.
One resorbable material of particular interest is marketed by Biomet, Inc. (Warsaw, Ind.) under the tradename LACTOSORB(copyright). LACTOSORB(copyright) is an absorbable co-polymer synthesized from all-natural ingredients: 82% L-lactic acid and 18% glycolic acid, unlike the homopolymers in common use such as 100% poly-L-lactic acid (PLLA) or 100% poly-glycolic acid (PGA), LACTOSORB(copyright) copolymer is substantially amorphous (i.e., without crystallinity), meaning that its degradation is uniform, precluding the crystalline release associated with degrading copolymers that have been associated with late inflammatory reactions. Furthermore, the LACTOSORB(copyright) copolymer ratio permits the polymer to retain most of it""s strength for six to eight weeks, which is appropriate for healing, but not so long as to raise concerns about long-term stress shielding of bone.
These polymeric resorbable devices may require xe2x80x9cmolding in the operating roomxe2x80x9d before they can be implanted. By way of non-limiting example, the minimum temperature for achieving a moldable condition generally is above the glass transition temperature (Tg) (approximately 57/60xc2x0 C.). During the heating stages of the resorbable materials, it is best not to allow the device (or any device possibly affected by water) to come in direct contact with boiling water. Because of this, It is difficult to raise the temperature of the resorbable device to above its glass transition temperature and to maintain the device above its glass transition temperature for long enough periods of time in the operating room to allow interoperative implant shape changes.
A need, therefore, exists for an apparatus and system which can raise a resorptive polymer material implant to above its glass transition temperature without exposing the implant directly to a liquid phase material. A need further exists for an apparatus and system which allows the resorbable material to be maintained above its glass transition temperature for an extended period of time. Further, a need exists for a heating device which is sterilizeable, as well as resusable.
In accordance with the teaching of the present invention, a device capable of heating resorbable material is disclosed having a pair of generally planar members. Each planar member defines at least one cavity which contains heatable fluid. The generally planar members are coupled by a hinge which allow the members to be rotated adjacent to each other so as to hold the resorbable polymer implant in close proximity to the heatable fluid. The temperature of the liquid stored within the cavity is elevated to above the glass transition temperature of a resorbable polymer. The resorbable polymer component which is to be surgically implanted in a patient is placed between the folded members and absorbs heat from the liquid stored within the cavity.
In one preferred embodiment, each member defines a shallow dish portion. Disposed above the shallow dish portion is a flexible polymer member which defines a fluid filled cavity therebetween. The fluid filled cavities are disposed adjacent to each other when the members are folded about the hinge, thereby holding the resorbable polymer component between two flexible polymer members, thereby increasing the surface area of the component in close proximity to the liquid.
In yet another preferred embodiment, the members define a cavity which is capable of accepting a fluid filled bag into a slot. The fluid filled bags can be heated prior to incorporation into the members through the slot.
In yet another preferred embodiment, the fluid filled bags are fastened to one surface of the foldable members using standard fabric fasteners. As with the other system, the fluid filled bag may be heated either prior to or after its adjoinment with the members.
The present invention provides a device which is capable of heating a resorbable surgical component and maintaining it above its glass transition temperature. The devices contain at least one fluid filled flexible sack, which functions to store heat energy to be transferred to the resorbable material through the flexible sack without submerging the resorbable material in a liquid. As a result, the aforementioned disadvantages associated with currently available resorbable material heating systems have been substantially reduced or eliminated.